Temperature controlling device



TEMPERATURE CONTROLLING DEVICE' Filed July 14, 1941 Patented Mar. 9,1943 UNITED STAT TEMPERATURE nnvroa James Hoekstra, Chicago,j.Iil'.,vassignor to Universal Oil Products Company, Chicago, 111., a,

corporation of'pelawalfe; e I Application Jui 14,;19l1, senai No.402,391 Claims. (c1; 236-18) This invention relates \Vto improvements inspecifically to an electrical system for raising orv lowering thetemperature of a furnace, stillv or like apparatus in response tovariations in temperature in said apparatus as detected by-a ,1

thermocouple positioned in the apparatus.

lbility and other desirable properties, thermocouples are widely used astemperature-sensitive" the form of an oscillator of the electronic tubedevices in the measurement and control of tem peratures, especially hightemperatures. How-, ever, the devices generally used with thermocouplesfor converting the variations of electro motive force of thethermocouples to physical actuations by which temperature control isactually eifected are costly and delicate.

' V supply relatively high plate vvoltage for such; means forcontrolling temperatures, andrefe'rs amplifier tube;

The unit I may, of course, comprise a-power transformer withaccompanying rectifier tube or tubes and appropriate filters, or, ifdesired, the

various plate and heater-currents may be supplied A I from any othersource of direct current of appro- Because of their small size, accuratereproduca priate voltage. v v

The unit 8 comprises a generator of low voltage alternating current andmay conveniently take type which generates an oscillating low voltagecurrent of about 1000 cycles per second. 0!

the function of the unit I, as will be hereinafter My present inventioncontemplates a device I designed to control the operation of heating orcooling devices in response to changes in electromotive force of athermocouple connected therewith, the device being characterized in thatitcomprises standard electrical parts such as resistcourse, with asuitable change of constants of the system other frequencies can beemployed, since described, is merely to superimpose an altemat- 'ingelectromotive force upon the direct current component set up by athermocouple.

If an electronic oscillator is employed, the heater current can besupplied through leads 8 which connect with leads 4 and the plate supplymay be drawn from one of the leads 5, the oathances, capacitors,electronic devices and the like,

The objects and advantages of my invention I will be apparent from theaccompanying drawing and following detailed description. 7

The single drawing is a schematic, partially diagrammatic, view of mysystem for controlling temperatures. e I I In view of the fact thatstandard units such as ode of the electronic oscillator tube beinggrounded at I0.

A thermocouple II is employed as a temperature sensitive device, one armof thethermocouple being connected to a potentiometer I2 through thevariable contact I 3. The potentiometer I2 is grounded, as at I4, andcarries a battery I2 or )other source of direct current electromotiveforce,

power packs, oscillators and amplifiers maybe employed with myinvention, and that such de J vices individually are available in manymodified, forms, for purposes of clarity and simplicity.

these devices will not be described in detail,;but will merely bereferred to in terms of their tune-:1.

tion since their varied forms are well known to the art, and theoperation of my device is not dependent upon any specific form of suchunits.

Referring in detail to the drawing, I indicates a conventional powerpack, designated PP which may be connected, as at 2 to a source ofalternating current, for instance, the usual 110 volt or 220 volt housecurrent. The unit I is grounded as at 3. From the power pack I leads 4may be drawn which carry low voltage current for the heaters of variouselectronic tubes which are employed in the system. Leads 5 drawn fromthe power pack I supply plate voltage for various electronic tubes usedin the system. Leads 6 may supply filament or heater current to a poweramplifier tube, if such is employed and leads -'I the battery being soconnected as to normally render the thermocouple negative when noelectromotive force is generated therein.

An electronic tube I 5, such as the conventional BSQ? (duodiode high-mutriode) is connected x into the system, the heater current beingobtained through leads I6 which connect with the leads 4,

and the cathode being connected through lead II to lead I8 which, inturn, connects with the positive side, of the battery I2. The diodeplates and control grid of the tube I5 are connected together and are,in turn, connected, through the resistances I9 and 20, to the normallypositive A lead 2 I ,carrying resistance 22 connects the oscillator 8 toa point, as at X, intermediate. resistances I9 and 20. One of the platecurrent leads 5 connects through resistance 23 to the normally positiveside of the thermocouple II, and lead 5 also connects with the plate oftube I5 through resistances 24 and- 25, the plate connecting throughresistance 25 and condenser 26 to the cathode of the tube.

In operation, the thermocouple II is inserted in the furnace, still orother device whose temperature is to be controlled. For a predeterminedtemperature a predetermined electromotive force will be set up at thethermocouple terminals. By an appropriate setting of the arm l3 thiselectromotive force can be balanced so that there will be no directcurrent potential at the point X. If the temperature is slightly belowthe adjusted temperature, the thermocouple electromotive force will beless than that of the potentiometer l2 and the point will have anegative potential with respect to the cathode of the tube 15.Superimposed upon this direct current component is the weak alternatingcurrent voltage from the oscillator 8. At a: this is, therefore, apulsating negative direct current potential. Since the grid and diodeplates of the tube l5 have a very high impedance to negative potentialsthe voltage drop through resistance 20 is relatively slight and theelectromotive force at :c is applied with negligible loss to the grid ofthe tube.

The output of tube I5 is connected to an amplifier 21 which may comprisean electronic tube amplifier of conventional construction, preferably oithe resistance coupled type, with any desired number of stages ofamplification. A power amplifier tube is preferably employed in the laststage. The heater current for the amplifier tubes may be supplied fromleads 4 and the heater cur-- rent for the power'amplifier tube may besupplied from leads 6. The plate supply for the power amplifier tube maybe supplied through leads i, and the plate supply for the prior stagesmay be supplied through the positive lead 5.

Connected in the output of the amplifier A, that is, in the platecircuit of the power amplifier, if an electronic tube amplifier isemployed, is a relay 28, the armature 29 of which functions to connector disconnect a power circuit 30 which includes a conventional controlunit 3i. The control unit 3i may comprise mechanism for opening orclosing a valve to admit fuel, steam or other energy medium to thedevice whose temperature is to be controlled and in itself constitutesno part of my invention.

Reverting to the operation of the tube l5, when the grid becomesnegative, as hereinbefore described, the pulsating component of theelectromotive force applied to the grid is then amplified by amplifier21 including the gain obtained in the triode section of tube 15. Theamplified alternating component of this electromotive force excites thegrid of the power amplifier tube comprised in unit 27 causing platecurrent to flow, thus energizing the relay 28 and turning on the heatsupply.

If the temperature goes above the point at which the instrument isadjusted, the thermocouple electromotive force will exceed that of thepotentiometer and there will be a positive potential at :1:. Of course,the alternating electromotive force supplied from the unit 8 will besuperimposed upon the direct current thermocouple potential. Since thegrid and diode plates of the tube l5 offer a relatively low impedance toa positive electromotive force, there will be a relatively large voltagedrop through the resistance 20 and a negligible portion of the potentialat a: will be applied to the grid. The output of the amplifier will thenbe insuflicient to excite the grid of the power amplifier tube in theunit 21 and the armature 29 of the relay 28 will open, thus turning ofithe heat.

It is obvious that with a predetermined setting of the potentiometer arml3, a predetermined temperature may be maintained constant. To

change the temperature at which a constant condition obtains it ismerely necessary to move the arm l3.

As an example of a system which has been found satisfactory, a duodiodehigh mu triode tube such as a type GSQ'Z tube may be employed as thetube IS. A 627G tube connected as an oscillator may be employed in theunit 8. The amplifier unit may comprise 6SC7 (double triode amplifier)and an 885 tube (gas triode). With an arrangement of this type the powerpack I may comprise a suitable power transformer and a rectifier withprovision for supplying the heater and plate currents to the varioustubes at the proper voltages.

Of course, other types of tubes, sources of low voltage alternatingcurrent and ultimate control mechanisms may be employed since myinvention is broadly directed to the modulation of the direct currentoutput of a potentiometer-thermocouple circuit and using the rectifyingaction of a sutiable electronic tube in such a way that the alternatingcomponent of the modulated direct current potential is amplified onlywhen the direct current potential is negative.

My invention is characterized in that: (a) it is economical to constructand maintain, (b) it is highly sensitive, since by modulating the outputof the potentiometer-thermocouple circuit an amplifier can be employedhaving a much higher voltage gain than couldbe obtained with a directcurrent amplifier which would be necessary if alternating currentmodulation were not used, (c) it is conducive to safety since breakageof the thermocouple or tube failure results in the heat being turnedoff, and (d) the device is portable and can be readily moved from placeto place without requiring leveling or special mounting.

I claim as my invention:

1. A device for controlling temperature which comprises a thermocouple,a source of direct current electromotive force of predeterminedmagnitude connected in opposition to electromotive force ofsubstantially equal magnitude generated by said thermocouple when thelatter is heated to a predetermined temperature, an electron tube havingat least three electrodes, the oppOsite side of said source of directcurrent electromotive force being connected to the cathode of said tube,means connected with the opposite side of said thermocouple forsuperimposing an alternating current electromotive force upon the directcurrent electromotive force of said thermocouple, means connecting saidlast mentioned side of said thermocouple to the control grid of the tubeto supply a pulsating potential to said grid, a resistance interposed insaid last mentioned connecting means for controlling the grid potentialin accordance with the relative magnitudes of said direct currentelectromotive force and the thermocouple electromotive force as thethermocouple temperature changes, means for amplifying the pulsatingplate-cathode potential of said tube, and means connected in the outputof said amplifying means for actuating a temperature changing mechanismto change the temperature of said thermocouple.

2. A device for controlling temperature which comprises a thermocouple,a source of direct current electromotive force of predeterminedmagnitude connected in opposition to electromotive force ofsubstantially equal magnitude generated by said thermocouple when thelatter is heated to a predetermined temperature, an electron tube havingat least three electrodes, the opposite side of said source of directcurrent electromotive force being connected to the cathode of said tube,means connected with the opposite side of said least three electrodes,the opposite side of said source of direct current electromotive forcebeing thermocouple for superimposing an alternating currentelectromotive force upon the direct current electromotive force of saidthermocouple, means connecting said last-mentioned side of saidthermocouple to the control grid of the tube to supply a. pulsatingpotential to said grid means interposed in said last mentionedconnecting means for controlling the magnitude of the grid potential ininverse proportion'to the current flowing in the grid-thermocouplecircuit, means for amplifying the pulsating plate-cathode potential ofsaid tube, and means connected in the output of said amplifying meansfor actuating a temperature, changing mechanism to change thetemperature of said thermocouple.

3. A device for controlling temperature which comprises a thermocouple,a source of direct current electromotive force of predeterminedmagnitude having its negative side connected to the negative side ofsaid thermocouple whereby said respective electromotive forces are inopposition and substantially equal to each other when the thermocoupleis heated to a' predetermined temperature, an electron tube having atleast three electrodes, the positive side of said-source of directcurrent electromotive force being connected to the cathode of said tube,means connected with the negative side of said thermocouple forsuperimposing an alternating current electromotive force upon the directcurrent electromotive force of said thermocouple, means connecting thenegative side of said thermocouple to the control grid of the tubeto'supply a pulsating potential to said grid, a resistance interposed insaid last mentioned connecting means for controlling the grid potentialin accordance with the relative magnitudes of said direct currentelectromotive force and the thermocouple electromotive force as thethermocouple temperature changes, means for amplifying the pulsatingplate-cathode potential of said tube, and means connected in the outputof said amplifying means for actuating a temperature changing mechanismto change the temperature of said thermocouple.

4. A device for controlling temperature which comprises a thermocouple,asource of direct current electromotive force of predetermined magnitudeconnected in opposition and substantially equal to electromotive forcegenerated by said thermocouple when the latter is heated to apredetermined temperature, an electron tube having at connected to thecathode of said tube, means connected with the opposite side of saidthermocouple for superimposing an alternating'current electromotiveforce upon the direct current electromotive force of said thermocouple,means connecting said last mentioned side of said ther-' mocouple to thecontrol grid of the tube to supply a pulsating potential to said grid, aresistance interposed in said last mentioned connecting means forcontrolling the grid potential in accordance with the relativemagnitudes of said direct current electromotive force and thethermocouple electromotive force as the thermocouple temperaturechanges, adjustable means connected with said source of direct currentelectromotive force for changing the relative potential of the cathodeand grid of the tube, means for amplifying the pulsating plate-cathodepotential of perature changing mechanism to change the temperature ofsaid thermocouple;

5. A device for controlling temperature which comprises a thermocouple,a potentiometer including a source-of direct current electromotive forceof predetermined magnitude, means connecting said latter through saidpotentiometer in opposition and substantially equal to electromotiveforce generated by said thermocouple when the latter is heatedto, apredetermined temperature, an electron tube having at least threeelectrodes, the opposite side of said source of direct currentelectromotive force being connected to the cathode of said tube, meansconnected with the opposite side of said thermocouple for superimposingan alternating current electromotive force upon the direct currentelectromotive force from said thermocouple, means connecting said lastmentioned side of said thermocouple to

